Modification of the tear function index and its use in the diagnosis of Sjogren's syndrome

Background-The tear function index (TFI) has been shown to be of value in t he diagnosis of patients suffering from Sjogren's syndrome. It is dependent , however, on introducing into the conjunctival fornix the correct concentr ation of fluorescein in at least one and a half times the normal tear volum e. The stimulus and effect of this added volume on the tear dynamics is lik ely to vary between individuals. These factors, together with the method of performing the test, limit its general applicability. Aim-To devise a method of performing the TFT with less variability and more general applicability. To present a theoretical and in vitro assessment of the dynamics of the TFI. Method-The study was divided into three parts. The first part was to compar e the results obtained using a prepared strip containing 1.3 mu1 of 0.5% fl uorescein with the introduction of the same amount of fluorescein as a drop , The second part was to compare the results obtained with prepared strips with the standard method of performing the TFT, both with and without topic al anaesthetic. The third part was an in vitro study of the rate of flow of graded volumes on a filter paper strip. 42 subjects with a diagnosis of Sj ogren's syndrome according to the European criteria and 126 without Sjogren 's syndrome were included. Results-There was no significant difference between the results obtained wi th a prepared strip and the introduction of 1.3 pi into the eye before perf orming the Schirmer's test and TFT (0.1<p<0.93). There was, likewise, no si gnificant difference between using the prepared strips and the standard met hod of performing the TFI (0.36<p<0.93). There was, however, less interocul ar difference (p=0.01) and variability (p=0.001) using the prepared strips than using a drop of fluorescein. Patients with Sjogren's syndrome had mean TFIs of 11.7 and 8.61 with upper 95% confidence values of 15 and 12 withou t and with topical anaesthetic, respectively. The theoretical calculation o f the TFI was similar to the observed values. The in vitro results allow th e filter paper to be removed from the eye at any interval and to estimate t he volume of tears that the filter paper was in contact with. Conclusion-The proposed method of performing the TFI is easy to perform, re liable, and therefore has general applicability for primary care and genera l practitioners. It allows the rapid identification of subjects who may be suffering from Sjogren's syndrome.